OKLAHOMA CITY (AP) — Security has been increased for Oklahoma Department of Corrections Director Robert Patton following threatening phone calls and emails that began after a botched execution in April.

The Tulsa World reported Sunday (http://bit.ly/1o3QsSM ) that records show the department bought a bullet-resistant sport utility vehicle at a total cost of $40,587. Patton is also accompanied by guards.

Department spokesman Jerry Massie said Patton does not have 24-hour security every day — only when he travels.

Massie said the threatening emails were sent to the agency’s Inspector General office. He said the phone calls could not be traced.

On April 29 convicted killer Clayton Lockett began struggling and convulsing during his execution. The execution was stopped — but Lockett died a short time later of an apparent heart attack.